Safety device for electrical detonators



y 1958 R. v. WALKER 2,835,877

SAFETY DEVICE FOR ELECTRICAL DETONATORS Filed May 31, 1955 Uited rates The present invention relates to an improved safety device for use with electrical detonators wired for remote control in demolition and blasting operations. Extremely sensitive to electric current, an electrical detonator presents an everpresent danger of explosion by even small electrical voltages or charges brought into contact with attached lead wires. In some instances, the static electricity in the body of a person coming in contact with an electric lead from a detonator can be sufficient to explode the detonator. Yet, handling of the leads in the field may be unavoidable. This, of course, is only one of the many ways in which a detonator may be exploded prematurely. The seriousness in this danger is multiplied understandably upon insertion of the detonator into a larger charge of explosive in preparation for a blast.

One object of the invention is to provide for repeated use with electrical detonators of the character recited an improved safety device of simple, practical construction which affords an increased measure of protection against accidental explosion from electrical causes, while also providing positive assurance against inadvertent or accidental shorting of detonator lead wires that might otherwise cause an operational failure of the normal firing procedure.

Other objects and advantages will become more apparent from the following description of the form of the invention illustrated in the drawings, in which:

Figure 1 is a plan view showing (partially sectioned) a safety device embodying the invention applied to electrical lead wires extending from a detonator inserted in an explosive charge to a manually operated generator;

Fig. 2 is a perspective view showing the components of the safety device and the detonator lead wires in partially exploded relation to each other;

Fig. 3 is a fragmentary sectional view on an enlarged scale taken generally along the line 3 3 of Fig. l; and

Fig. 4 is a fragmentary sectional view on an enlarged scale taken generally along the line 44 of Fig. l.

in use the safety device It) embodying the invention is applied, as shown in Fig.1, to the two electrical leads y 12., 14 extending from an electric detonator 16 of conventional construction. After attachment of the safety device, the detonator 16 is inserted into a charge 18 of dynamite, TNT, or similar explosive. The ends of the leads 12, i4 remote from the detonator 16 are attached to the terminals 2d of a hand generator 22 or other suitable source of electric voltage customarily used in blasting operations.

structurally the improved safety device comprises, as shown more clearly in Fig. 2, a rectilinear insulating block 24 formed in upper and lower half sections 26, 28

of plastic or other suitable insulating material. The top of the lower block section 28 forms a generally flat face 34) opposing a similar flat face 32 on the underside of the upper block section 26. A spaced parallel pair of semi-cylindrical grooves 34 defined in the upper face 30 of the lower block section 28 extends longitudinally across the block section in opposing relation to a generally similar pair of longitudinal grooves 36 defined in the lower face 32 of the upper block section 26.

Upon placement of the two block sections 26, 28 together with the generally fiat faces 30, 32 opposing each other, the opposing grooves of the upper and lower pairs 36, 34 define together longitudinal bores denoted by the same reference numerals, Figs. 3 and 4, extending longitudinally through the block 24 for the reception of the two wires 12, 14, which project beyond opposite ends of the block 24 as shown in Figs. 1 and 2.

The medial portion of that segment of each Wire 12, 14 contained within the block 24 is bared by the removal of insulation. The bared segment 38, Fig. 1, of

the wire 12, for example, has a length somewhat lessthan one-half that of the block 24 along the wire.

The lower face 32 of the upper block section 26 defines a downwardly open groove or bore 40, Figs. 2, 3 and 4, extending from one side of the block section transversely across the medial portion of the face 32 in substantially perpendicular relation to the grooves 36. A similar groove of lesser depth 42, Figs. 2 and 3, is formed in the lower block section face 30 in opposing relation to the upper groove 40. Upon placement of the two block sections 26, 28 together, the two grooves 40, 42 provide a receiver for a cylindrical, bare metal stem 44 of a removable safety element 46. See all four figures.

As shown, the bare stem 44 seats in the upper transverse groove 40 in overlying relation to the bared segments of the leads 12, 14 extending through the block 24. The thickness of the stem 44 is somewhat greater than the depth of the groove 40.

Structurally, the stem 44 is the longer portion of a straight shank (denoted by the same reference numeral) extending laterally from the block 24 and joining with the medial portion of a T handle 45, Figs. 1 and 2. The shank and handle together constitute a T-shaped safety element 46. The entire surface of the safety element 46, except for the stem portion 44, which extends into the block 24, is formed by an insulating material 50, Fig. 2.

The two block sections 26, 28, are separably held in face to face opposing relation to each other by a bolt 52 passing downwardly through the upper block section 26 between the lead wires 12, 14 and threaded into the lower block section 28.

In preparation for application of the safety device 10 thus formed to two detonator lead wires 12, 14, the insulation is removed from short side-by-side segments of the wires. The connecting bolt 52 between the two block sections 26, 28 of the device is unscrewed or loosened to permit separation of the two sections sulficient for lateral insertion of the two electrical. leads 12, 14 into the opposed pairs of grooves 34, 36. The stem 44 of the safety element 46 is seated in the upper transverse groove 44 in overlying relation to the bared segments of the leads 12, 14.

Tightening of the bolt 52 clamps the bare metal stem 44 hard against the bared segments of both lead wires 12, 14, Figs. 1, 3 and 4. Sufficient pressure can be applied through the block segments and the stem 44 to deform the adjacent portions of the leads 12, 14, pressing.

the latter hard against the stem to positively assure short circuiting of the leads.

In connection with the contact effected between the stem 44 and both leads 12, 14 in the manner recited, it will be appreciated that the T-handle 45 on the safety element 46 provides to the user a convenient means of applying substantially the full strength of his arms in subsequently extracting the stem 44 front between the two block sections. Because of the facility and advantage with which force can be applied in withdrawing the safety element 46 from the block 24" in this manner, a highorder of clamping forces can be applied between the stem'44 and the two electrical leads to positively assure a short circuit through the safety device. The short circuit assured by the powerful clamping forces of the stem 44 on both leads 12, 14, provides increased protection' against explosion of the detonator 16 by a voltage inadvertently applied to the leads.

The protection afforded in this manner is further increased by the complete insulation from the external environment of the exposed segments of the leads 12, i4 exposed for contact with the stem 44. As previously mentioned, these exposed segments of the leads are contained entirely within the insulating block 234. More over, the entire surface of the safety element 46 projecting from the block is insulated; Hence, extraneous voltages are prevented from entering either electrical lead through the safety device.

As previously intimated, the T-handle 45 of the safety element 46" provides for easy removal of the safety ele ment from the block 24 even though powerful clamping forces-may be applied between the stem 44 and the cared segments of the leads 12, 14. Ordinarily the safety elen1ent'46 is removed from the block 24 only a short time before actuation of the generator 22 to explode the detonator'ld. However, even after removal of the safety element 45, the exposed segments of the leads E12, 14 are'still insulated from contact with the exterior environment by the block 24, thus providing a measure of continued protection against premature firing.

Moreover, the block 24 holds the bared segments of the electrical leads f2, 14 separated from each other after removal of the safety element 45, thus positively preventing accidental short-circuiting which could interfere with normal firing of the detonator 16 by subsequent operation of the generator 22; Thus, the improved safety device 10 not only provides an additional degree of safety against'premature explosion of the detonator but also adds to the certainty of firing by the normal firing procedure carried through after removal of the safety element 46.

Well suited for repeated use over a long service life, i

the safety device 10 thus provided is extremely simple in construction and well'suited'for most economical manu facture.

WhileI have shown and-described a preferred embodiment of'my invention, itwill be apparent that'numcrous variations and modifications thereof may be made without departing from the underlying principles and scope ofthe invention. I therefore desire, by the following claims, to include all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. A safety device for repeated use with electrical detonators wired for remote control, comprising, in combination, an insulating block formed in two half sections of insulating material each defining a generally fiat face thereon opposing a generally similar face on the other section for separable engagement therewith along a central longitudinal plane of the block, said half sections each defining in said face thereon a spaced parallel pair of semi-cylindrical grooves extending longitudinally thereacross in opposing relation to generally similar grooves in the face of the other section, said opposing pairs of grooves in-the fiatfaces of both half sectionsproviding upon placement of saiclsections together space thcrebetween for reception of two detonator leads, at least one ofsaid sections defining a transverse groove therein extending substantially-acrossthe face thereof from one side thereof in perpendicular relation to said longitudinal grooves therein, a T-shaped safety element including an elongated handle and a shank integral with the central portion of said handle and projecting away therefrom in perpendicular relation thereto, the portion of said shank beginning some distance from the handle and extending to the extreme end of the shank opposite the handle constituting a bare metal stern having a length approximatcly equal to the width. of said block, said stem being adapted to extend extraetably along said transverse grooveinto said block between said sections thereof and having a transverse thickness substantially greater than the depth of the transverse groove to press against detonator leads in the adjacent portion of the longitudinal grooves, the surface of said safety element except for said stem being formed completely by insulating material, and a bolt separably securing said block sections together.

2. A safety device for repeated use with electrical detonators Wired for remote control, comprising, in combination, an insulating block formed in two sections of insulating material each defining a face thereon opposing a generally similar face on the other section for separable engagement therewith, at least one of said sections defining in said face thereon a spaced pair of grooves extending thereacross, said grooves providing upon placement of said sections together spaces therebetween for the reception of two detonator lead wires, at least one of said sections defining a transverse groove therein extending substantially across the face thereof from one side thereof in crossing relation to said first mentioned grooves, a safety element including an insulated handle portion and a shank portion extending from said handle portion, said shank portion ineluding'a bare metal stem adapted to extend extractably along said transverse groove into said block between said sections thereof for engagement with detonator lead Wires disposed in said first mentioned grooves, and means separably securing said block sections together.

3. A safety device for repeated use with electrical detonators wired for remote control, comprising, in com bination, an insulating block formed in two half sections of insulating material, each section defining a face thereon opposing a generally similar face on the other section for separable engagement therewith, one of said sections defining in said face thereon a spaced generally parallel pair of grooves extending thereacross, said grooves providing upon placement of said sections together spaces therebetween for the reception of two detonator lead wires, at least one of said sections defining a safety element groove therein extending from one side thereof along the face thereon in crossing relation to said first mentioned grooves, a T-shaped safety element including an elongated handle and a shank intergral with the central portion of said handle and projecting away therefrom in perpendicular relation thereto, a portion of said shank beginning some distance from the handle and extending to the extreme end of the shank opposite the handle constituting a bare metal stem adapted to extend extractably along said safety element groove into said block between said sections thereof and having a transverse thickness substantially greater than the depth of said safety element groove, the surface of said safety element except for said stem being formed entirely by insulating material, and means separably securing said block sections together.

4. A safety device for use with electrical detonators wired for remote control, comprising, in combination, an insulating block formed in two sections of insulating material each defining a face thereon opposing a generally similar face on the other section for separable engagement therewith, said faces of both sections together defining a spaced pair of grooves extending across said block to provide upon placement of said sections together spaces therebetween for the reception of two detonator lead wires, one of said sections defining a transverse groove therein extending substantially across the face thereoffrom one side thereof in crossing relation to said first mentioned grooves, a safety element including a bare metal stem adapted to extend extractably along said transverse groove into said block between said sections thereof for engagement with detonator lead wires disposed in said first mentioned grooves, means separably securing said block sections together, and handle means connected with said stem for extracting the latter from between said block sections while the latter remain secured together.

References Cited in the file of this patent UNITED STATES PATENTS 

